Our Cummins C-8.3 engine has a fuel shut off activated by a solenoid, which pulls-up with starter and holds-up with ignition.
We found the solenoid was not opening fully which caused our engine to exhibit low-power and only moved motorhome at low speeds due to fuel starving.
We could remedy the problem by manually pushing up solenoid when engine was running. A plastic cable tie could assure that fuel valve stays open, but it will also prevent engine stopping even with ignition key off.
Solenoid has two internal 12 volt coils. A light magnet force is powered by ignition key, but the force is not enough to pull-up against the internal spring and injector pump. A very strong magnet force is powered from starter circuit, which has enough force to snap the fuel valve open. When the starter motor is disengaged, the light magnet force will keep fuel valve open without overheating the fuel solenoid. A relay is also used in the circuit.
We removed original solenoid and mounting bracket and installed a new bracket and new solenoid.
Original Bracket Removed
Cummins part number 4089574 fuel solenoid kit has all the parts including new attachment bolts. Cost is $300 garage price and about $400 consumer price. New solenoid is larger and has improved construction.
New and Old Solenoid
It is important to adjust solenoid pull-up length correctly. Solenoid must be able to fully pull-up its movable core so it will stay up with just ignition coil. And at solenoid fully open position the injector pump fuel shut off valve must be also be fully open to insure full fuel flow from lift pump.
New Installed Fuel Solenoid
Fuel Shut Off Relay Diagram
Cummins 300hp 8.3 Fuel System Overview